This technical note presents an over view of the flight characteristics of Unmanned Air Vehicles (UAV’s). The research focuses on the various types of UAV before moving on to the associated technical requirements and innovations. The categories discussed cover flight control, navigation, propulsion, payload capability, launch and recovery, communications and airspace management. To conclude, current and future UAV development issues are also explored in light of the political and economic market.

Introduction

HE development of unmanned air vehicles has been greatly accelerated in the past decade. Major aerospace organizations have seen the flexibility of application of such vehicles in a military or battle field situation. This will inevitably do away with the high casualties associated with conflict scenarios.

There are three groups of UAV:

1. High altitude and long endurance (HALE).
2. Medium altitude and long endurance (MALE).
3. Tactical role referred to as TUAV.

A combat UAV i.e. a UCAV can fall into any of the three above categories

Flight Characteristics

Flight Control

Typically a UAV is operated by:
1- A flight control (designated pilot).
2- A payload control (sensor operator).
3- A command control (mission controller).
4- A maintenance control (ground crew).

Each controller or operator has a different level of control falling into the categories below:
1- Operators function all aspects of the UAV. (current situation)
2- Operators function only partial aspects of the UAV. (current situation)
3- Operators do not function any aspect of the UAV i.e. fully autonomous. (future)

The flight control is performed by specially trained pilots using point-and-click style interfaces. For example, Sweden has a UAV pilot training program which provides the opportunity for both aircraft pilots and newly graduated pilots to acquire the essential skills needed to fly a UAV from the ground.

Navigation

Unmanned air vehicles usually incorporate global positioning satellite (GPS) systems for navigation. These systems use pre-programmed way points which can be modified by the mission controller allowing for quick and effective mission changes. Examples of UAV’s using such a system include the Predator2 and Global Hawk3. Some UAV’s will use terrain mapping which is also utilized in some modern day combat aircraft, for example the Tornado. Such a system however suffers from the need for 3-d digital maps of the global terrain which itself can be a technological barrier. The remainder of UAV’s may use SLAM algorithms (Simultaneous Localization and Mapping), trajectory planning (establish safe paths with inter-linking) or autonomous navigation planning. The SLAM algorithm is commonly seen on HALE and MALE types of UAV whereas
the trajectory planning is still somewhat in development since the optimization of safe flight paths is still in the research phase. Autonomous navigation planning implies the sharing of way points and related co-ordinates from one UAV to another.

Propulsion

Piston or electric engines are commonly observed on UAV’s. Turboprop and turbojet engines are more suited to HALE and MALE types of UAV. There are new innovations in the area of UAV propulsion especially focused on improving UAV endurance. Such innovations for example, regenerative fuel cells, solar and nuclear4 power are envisaged to give long operational life for the UAV’s.

Payloads

Most aircraft payloads can also be carried by UAV’s. The restrictions here pertain more to a scaling problem i.e. the size of the payload and the corresponding availability of a UAV to transport it. For TUAV’s miniaturization of payloads has already been researched where payloads have been appropriately scaled down. Micro-UAV’s5 are currently being research for military use.

Launch and recovery

A runway or flat open site is used for both the launch and recovery of HALE and MALE types of UAV. In such cases no pre-flight assembly of the UAV is required. For TUAV’s a RATO (rocket assisted) system6 or a catapult system (from a rail) is used for take-off. The recovery of such UAV’s is performed using an airbag or parachute. TUAV’s typically require pre-flight assembly. Other methods of launching UAV’s include air launching from under an aircraft wing (like a conventional missile), helicopter launching or even VTOL (vertical take-off and landing)7. The developments in this field are currently on hold with no recent innovations of interest.

Communications

Modern day UAV’s use dedicated control link interfaces between vehicle and operator controller. This may include satellite UHF (or Ku) bands for both long range and short range. The payload communication with the ground controller is separate from the main UAV control link. In any case a failure mode has to be built into the UAV to allow for control link failure and enabling it to operate autonomous if required. A moving platform can also be used to control some UAV’s. Examples include ships and aircraft with respective voice communication architecture.

Air Traffic Management

The issue of air traffic management for UAV’s lags well behind the actual developments and capabilities of the UAV’s. As such there are no rules which have been exclusively specified for UAV air traffic management. The UAV’s themselves have been built to a high quality standard, for example the Global Hawk has a certificate of authorization whereas the Predator is built to an expected quality standard based on the manufacturer’s best guess, but there is still an on-going certification and conformity rule set which needs to be established. In the United States, UAV’s come under the laws for experimental aircraft or test aircraft. In Sweden there has been more progress with UAV’s being included in military aircraft certification laws. For the majority of nations however, UAV’s are still confined to flying in restricted airspace. New legislation and certification is thus an on-going process for UAV’s8.

Discussion and Conclusions

The future of UAV’s definitely looks bright and eventful. Given the current conflicts worldwide, UAV’s have a definite part to play from a military perspective. Commercialisation of UAV’s in the civilian sector will however take longer due to both technology adaptability, UAV terminology {9} and public perception. This stems from the current UAV incident rate which is 1 in 1000. This incident rate needs to be improved to 1 in 100000 for some public confidence. Furthermore, the issue of funding, liability, safety, insurance and certification are all on-going processes for UAV’s
thus amplifying the public concern for such vehicles to be used for civilian purposes. In terms of funding, the United States has the most dedicated funds for UAV research and development closely followed by Europe. Australia also has some dedicated funding for UAV research through large corporate firms10. The rest of the world however contributes very little to UAV research and development. It is expected that the military will hence drive the UAV requirements for 20-30 years before a shift to the civilian sector.